1. Field of the Invention
The present invention generally relates to a drive control device for a stepping motor to produce mechanical rotation dependent on steps from one angular position to another, and in particular to a drive control device for controlling a microstep drive of a stepping motor capable of smoothly rotating with a high accuracy in angular positioning by increasing the number of steps without requiring a high speed processing of a microcomputer in generating a step signal.
2. Description of the Prior Art
In recent years, a microstep drive of a stepping motor is realized by an open-loop control system by way of converting digital signals to mechanical rotation, and since a servo mechanism can be easily constructed with high accuracy without providing a feedback component such as an encoder or potentiometer, a microstep drive of a stepping motor is widely used as a drive power supply for driving, e.g., a magnetic recording head of a magnetic disk device and other various apparatuses. In such a wide utilization, a stepping motor serves as a link or interface between computers and mechanical devices,having an extensive usage in equipment coupling to computers, such as printers, plotters, magnetic memory disks and the like, providing very accurate mechanical positioning without any feedback, and thus the stepping motor can be used in various automatic control systems, home and office appliances, audio/video apparatuses and the like.
Conventionally, there has been proposed a drive control device for a stepping motor as disclosed, for example, in the Japanese patent unexamined laid open publication 343294/1994 in which a rotation for each one pulse is corrected to be uniform in microstep driving of a stepping motor.
In the disclosure of this conventional construction, as shown in FIG. 5, in microstep driving of a stepping motor 1, a step signal "i" of pulse clocks indicating steps for each angular position generated by a step signal generator (not shown) is counted up or down by an up/down counter 2 in accordance with a rotational direction signal "h" indicating a rotational direction of the motor to thereby generate count value data. The count value data output of the up/down counter 2 is applied to ROMs 3a and 3b storing an exciting signal data corresponding to the count value data. Thus, the count value data is used as address data for the exciting data stored in the ROMS. The exciting signal data stored in ROMs 3a and 3b is read out therefrom and then converted to analog voltage signals by means of D/A converters 4a and 4b, and then the converted voltage signals are amplified by means of drive amplifiers 5a and 5b to thereby drive the stepping motor 1.
In this arrangement, the exciting signal data of the ROMs 3a and 3b is converted to an analog form of dummy sine wave to increase the number of steps for one rotation of the stepping motor. By increasing the number of steps for a unit rotation, the accuracy of the step angular positioning can be made higher together with attaining a smooth rotation of the stepping motor.
In the conventional construction, however, in order to obtain a high accuracy of the step angular positioning together with smooth rotation of the stepping motor, it is necessary to increase the number of steps for the angular positioning and the number of divided segments of the dummy sine waves. Thus, the number of steps for rotating the stepping motor to a target position is increased, and therefore a microcomputer included in the step signal generator (not shown) is required to have a higher speed processing performance, which arises a problem of a high cost in constructing the drive control device.